Fix default openshift configuration for language

Fixes #1027
Signed-off-by: Michal Čihař <michal@cihar.com>

weblate/settings_openshift.py

@@ -103,7 +103,7 @@ else:
 # Where to put Whoosh index
 WHOOSH_INDEX = os.path.join(os.environ['OPENSHIFT_DATA_DIR'], 'whoosh-index')
 
-SOURCE_LANGUAGE = 'en-us'
+SOURCE_LANGUAGE = 'en'
 
 # List of machine translations
 MACHINE_TRANSLATION_SERVICES = (